Thermal demand meter



April 4, 1939. P. M4 LINCOLN ET A1.

THERMAL DEMAND METER 3 Sheetyheet l Filed April 30, 1936 April 4, 1939.' M P. Mi LlNoLN ET AL. i M 2539 y Y THERMAL DEMAND METER Filed April 30, 1956. 5 Sheets-Sheet 2 April 4, 1939. P. M. LINCOLN ET AL l 2,153,091

THERMAL DEMAND METER Filed April 50, 1936 5 Sheets-Sheet 5 Load Patented Apr. 4, 1.939 i uNiTED "sTATEs 42,153,091 THERMAL DEMAND amm Paul M. lincoln and Robert B. Sprole. Ithaca,

NJY.: said Sprole assisnor to said Lincoln Application April 30, 1936, Serial No. 77,108

120mm (c1. rxr-e5) The principal objects of this invention 4are toimprove the construction of the'thermal demand meter so as to reduce to the minimum the errors due to inadequately controlled radiation land l convection of heat and to provides structure in which the Arate of heat exchange per degree of temperature difference between' the two operatingelements'will be uniform at various temperature dierences.

l A further and important feature of the invention consists in producing a structure which is capable of being reproduced in quantities with,

great accuracy.

1B sist in the novel construction of pressure fluid reservoirs .which are connected to a Bourdon tube V structure .for operating an indicator, and in the novel construction and arrangement of electrical resistances or heaters and .the means em- 20 bracing the same, whereby said heaters are maintained in uniform close-engaging contact with said reservoirs, and further, in means applied to said heaters and reservoirs to eifectthe equalizing and distribution of the heat therein and con- 25 trolling the dissipation of the heat generated.

A further important feature consists in the novel features of construction and the method of assembly whereby the several elements may be `ce) one ofthe heating elements as shown'assembled in Figure 1 Figure 4 is an enlarged cross sectional view through one of the heater elements. l Figure 5 is an enlarged. cross. sectional view 46 through one of the heaters showing the copper conductors.

`ligure 6 is a view similar to Figure 1 Showing va structure as applied to the measurement of a polyphase current. y 50 Figure 7 is an enlargedI cross section through one of the translating devices shown in Figure 6; Figure 8 is an enlarged-perspective detail of one of the he'aters shown inl Figure 6. n

lFigure 9 is an enlarged cross section of one 65 of the heaters shown in Figure 6.

Figure 10 is al diagrammatic view illustrating lthe fundamental theory. of Vthe thermal watt'-J meter. 1

Figure 11` is a longitudinal mid-sectional view of a modified form of fluid reservoir having a 5` double re-entrant head. v a

In the use of thermal type metersthere are numerous elements which tend toward error in translating the efl'ect o'fqthe transformed electric energy being measured and the present invenl0 tion has been devisedy particularly to reduce these uncertain elements to a condition of substan tial uniformity. The principal features of the invention con- It has been proposed -to translate the effect of heat produced bythe flow of electric current into 15 fluid pressure and to operatethe designating indicator with such fluid pressure, using Bourdon t tubes or other means to operate the indicator.

It has also been proposed to enclose the fluid' and the electric heating elements, within vacuum tubes to reduce error caused by lradiation and convection.

The present invention proposes the use of both of these features andincorporated novel constructions and arrangements as hereinafter,de'

scribed. l

In the application of the invention herein shown the reservoirs Iufor containing an expansile fluid are preferably formed of steel drawn into tubular form having a roundedA closed end 2.

The head 3 for closing the open end of the reservoir is also preferably formed of drawn steel to fit tightly into the end of said reservoir, the edges ofthe head and reservoir ,l being sealed by. welding, brazing or soldering.

The use of a re-'entrant type of head for the cylindrical reservoir ensures the presentation of a desirably'large cylindrical'surface on its exterior, relative to the uid capacity of the reser- 40 voir and this effect may be further enhanced by the use of a double re-entrant head 3 and l2.. that is to say, the cylinders may each advantageously comprise a tube with a head inserted at each end as exemplied in Figure 11.

Each reservoir I is provided with a capillary tube i connected to the head and leading to a "Bourdon" tube 5 which is connected by the operating arm 6 to an indicator spindle 1 operating 50 over a scale l'. r

'In the form illustrated in Figure 1 the reser- Voirs l are each inserted into one end of a tube 6 which is preferaby formed of vulcanized fibre or other suitable material which will transmit 55 heat generated by thermal meter resistance heaters and not be detrlmentally aiected thereby.

A resistance member or heater 9 formed of a metal sheet of predetermined resistance value is bent around each tube 8 fitting snugly thereto. These heaters are eac formed with a longitu dinal slot Ill arranged centrally of the Width thereof and extending for the major portion of the length, and conductor strips II and I2 preferably of thin sheet copper are secured to the bifurcated ends of the heaters.` These copper strips preferably but not necessarily overlap each other and a thin sheet I3 of electric insulating 'material is inserted between the overlapping portions a-nd extends into the slot I0 of the heater.

Each heater and its attached conductor strips is bound securely against the cylindrical surface of thetube 8 and a covering I 4 of a suitable insulating material such as a synthetic resin is moulded thereover to form a unitary insulating cover. It will be further evident that the entire heater structure may be moulded into a single unit of any suitable mouldable plastic material such as Bakelite.

A sleeve I5 of metal of high heat conductivity, preferably copper, `may be arranged to .closely surround the insulating cover I3 to encircle the heater 9 and to extend Well over the connecting ends of the copper conductors, thus forming a heat conducting member to absorb heat conducted outwardly from the heater and acting as a distributor taking heat from hotter portions of the resistances and distributing it to portions having lesser heat evolution and also conducting outwardly conducted or radiated heat from the tion and radiation losses, the only heat con' duction from the heaters being through the copper leads, which are connected by suitable wiring to the meter circuit I1, which is of a well known thermal meter type and in Figure 10 there is shown a circuit diagram illustrating the basic theory of the thermal wattmeter which may be briefly referred to as follows:

In the said diagram a source of electrical energy is shown supplying aload. Incorporated within the meter is a small transformer T which has a secondary voltage E. R are two equal resistances through which currents are circulated in the following manner. It is obvious that the voltage E will-set up a current throughthese two resistances which is equal to The load current is also caused to pass through 'these same resistances and it is obvious that one-r half of. this load current will pass through each resistance (resistances equal). It is also obvious as shown' bythe arrows in Figure 10 that these currents, one due to the presence of the voltage E and the other the load current arealways additive in one resistance andsubtractive. in the \other. Y The resulting heat liberated in one resistance is obviously where is the phase angle between the cur rent 2R and Athe current In the other resistance the resulting heat will obviously be `the'thin tubes 8 imparting heat to the cylindrical reservoirs I thereby expanding ther liquid which is enclosed therein and creating pressuresl which are transmitted through the capillary tubes 4 to effect the diaerenuai dilation of the Bourdon tubes in direct proportion to theflow of energy and producing a corresponding movement of the indicator spindle 1.

It will be understood that as the only escape for the heat generated in the heaters 9 is through l the copper leads or conductor strips Il and I2 and the capillary tubes 4, the cross sectional 'area and length of such leads may be varied to definitely regulate the time period of response. The heaters 9 are of relatively small cross section and lowheat conductivity compared to the leads II and I2 and there is normally considerable variation in the temperature of the heaters at various points, the ends farthest from the leads being the hotter. By embracing the heater structure with the conductor sleeve I5 as described, the heat ultimately applied to the reservoir I is substantially uniform. So also the use of the sleeve I5 has a very beneficial effect in equalizing the temperatures throughout the mass of the insulating material. The use of the sleeve I5 is preferable but not necessary. y

Another and important effect produced by the use of the embracing heat conductor sleeve, is, that it will unify the rateof heat exchange per degree of temperature difference which is not entirely uniform at various temperature differences which exist in various parts of the electricinsulation.

The structure herein. described maybe varied considerably in respect to the actual formi or arrangement of the heaters and the insulationthereof as will be seen by the structure illustrated in Figures 6 to 9 whichv illustrate the application of the invention for use in polyphase circuits.

In the structure shown in these figures, each of the iluid cylinders I has arranged in proximity thereto, two or more heaters I9 each of which is formed similarly to the heaters 9 and each being provided with heat conducting leads 20 and 2| which are suitably wired to the transformers of the meter circuit.

'I'he heaters as herein shown are arranged in the part cylindrical recesses 12 arranged in the outer wall oi' a cylindrical member 23 of insulating material in which the fluid-containing cylinder I is located. The heaters are separated by longitudinal ribs 24 and are enclosed by part cylindrical shields 25 of insulating material which are bound securely in contactv with the heaters by the enclosing conductor sleeve 2.6' of copper or other suitable heat conducting material.

The transfer of heat to each of the cylinders i is effected from. the several .heaters surrounding such cylinders and the unication of the heat' applied andthe regulati of the heat escape is eiiected in the manner described in respect to the structure previously described as of a single phase meter circuit.

We claim: y

1. In a thermal electric'meter the combination with a iiuid pressure actuated indicator mechanism including sealed reservoirs, of electric heaters of sheet metal insulated from and arranged to closely embrace said reservoirs, sheet metal conductor leads of a higher heat conductivity than said heaters secured to and leading from said heaters, and aheat conductor sleeve surrounding said heaters and a portion of said conductors.

2. Ina thermal electric meter the combination with a iiuid pressure actuated indicator mechanism including sealed reservoirs, of electric heat-l ers of sheet metal slotted from one end, sheet metal conductor leads connected to the bifurcated ends of said heaters, sheets of insulation between said leads extending into the slots in said heaters, and metal sleeves surrounding saidheaters and the ends of the conductors connected therewith.

3. In a thermal electric meter the combination' with a iluid pressure actuated indicator mechanism includinga sealed cylindrical reservoir, of an 1 electrical resistance element composed of a thin and closely embracing the periphery oi said cylindrical reservoir..

5. In a thermal electric meter, the combination with a huid pressure actuated indicator mechanism including a sealed cylindrical reservoir, a pair oi' semi-circular'resistance heaters'peripherally applied over said cylindrical `reservoir and insulated the one from the other.

6. In a thermal electric meter the combination with a iluid pressure actuated indicator mechanism including a sealed cylindricalreservoir, a

pair of semi-circular resistance heaters peripherally applied over said cylindrical reservoir in a substantially concentric path thereabout and being peripherally spaced and electrically isolated/ within said senil-cylindrical cavity and abutting said rib at the end in positioning contact.

8. In a thermal electric meter the combination with a fluid pressure actuated indicator mechanism including a sealed cylindrical reservoir, an insulating sleeve snuglyy tting over said reservoir and formed with semi-circular cavities spaced by longitudinal perlpherally spaced ribs, a separate semi-cylindrical electric resistance heater titting snugly in each of said semi-circularcavities and separated the one from the other by said vspaced ribs, semi-circular shields applied over said heaters in said semi-circular cavities, and means applied over said semi-circular shields and holding the same in conning relation against said recessed heaters.

9. In a thermal electric meter, fluid pressureactuated indicator mechanism including cylindrical uid reservoirs adapted to be heat-iniluenced, and closure means retreating inwardly from opposite ends of said cylindrical reservoirs v in displacement relation to the fluid body.

l0. In a thermal electric meter the combina-- tion with a fluid pressure actuated indicator mechanism including sealed reservoirs, of electric heaters having substantially half oi' their radiating surface disposed in intimate thermal contact with said reservoirs with the minimum thickness of insulaton therebetween.

11. In a thermal electric meter the combina` tion with a iluid' pressure actuated indicator mechanism including a sealed reservoir, ofseparate electric heaters arranged in close thermal contact with said reservoir and each subject to' inherent local temperature dierences, said heaters being disposed on opposite sides oi' the reser` voir respectively, and heat-conducting means bridging said respective heaters and effecting a distribution of the heat from the hottest zoneto the coolest zone of each of said heaters and from one heater to another to maintain a substantial thermal balance therein.

12. In a thermal electric meter the combination with a, fluid pressure actuated indicator mechanism including sealed reservoirs, of electric heaters comprising strips of thin resistance metal bound securely upon the' outer surface oi' said reservoirs in extensive and intimate thermal relation.

PAUL M. LINCOLN.

ROBERT R. BPROLE. 

